1. Technical Field
The present invention relates to antenna pattern shaping structures and, more particularly, relates to antenna pattern shaping structures for portable radios.
2. Description of the Related Art
Cellular radio telephones typically have telescopic or stubby antennas. Such telescopic antennas in the up position typically are half wave antennas. Such stubby antennas and telescopic antennas in the down position typically are quarter wave antennas.
Stubby antennas and telescopic antennas in the down position are known to be less efficient than telescopic antennas in the up position. This is because stubby antennas and telescopic antennas in the down position have antenna patterns typically produced by two quarter wave elementsxe2x80x94first a helix in the stub and second the radio circuit board itself.
More efficient antennas increase radio performance because they are capable of pulling in weak radio signals. Efficient power transmission between antenna elements in a radio system can be increased by shaping the gain patterns of the antennas. Optimum gain pattern shapes of antennas look for signals where they can be best received. They also conserve portable battery capacity by focusing transmit energy in more optimum directions.
An effective way of improving the efficiency of stubby antennas and telescopic antennas in the down position on handheld portable radios is needed.
An efficient antenna pattern shaping structure employs a parasitic element of a conductive surface next to radio circuitry to shape an associated antenna, preferably one that is a quarter wave antenna. The parasitic element is disposed on a first side of the radio circuitry to act as a reflector of electromagnetic energy. The parasitic element has at least two edges and wherein the at least two edges of the parasitic element are bent in a direction towards the radio circuitry in order to shape the antenna pattern more efficiently. The parasitic element is electrically slightly larger than a half wavelength of a frequency band of interest, preferably the low frequency of interest. An optional opposing parasitic element can be disposed on a second side of the radio circuitry opposite the first side. The opposing parasitic element is electrically slightly smaller than a half wavelength of the frequency band of interest, preferably half a wavelength of the high frequency of interest. A conductive surface, having bends at the ends and preferably grounded, on a side of a wiring board of the radio circuitry, can be used in addition to or instead of an independent parasitic element.
The details of the preferred embodiments of the invention will be readily understood from the following detailed description when read in conjunction with the accompanying drawings wherein: